requirement prioritization

Requirement Prioritization

Requirements Prioritization


Structure of the presentation

Introduction

Prioritization principles

Prioritization methods

Prioritization scales

Wiegers` method

Pair-wise comparison technique

Comparison between the methods


Introduction (1/3)

There are usually more requirements than you can

implement given stakeholder`s time and resource

constraints... [Kar97],

Lot`s of requirements

Few resources

but...


Introduction (2/3)

... on the other hand, systems have useless

functions for the users and customers!

Large amount of the software functions are ”rarely” (19%) or ”never used” (45%) [Moi00]


If we manage to implement just those requirements that

meet customer and user needs

product development time shortens

product development costs decrease

”How to select a subset of the customers´ requirements and

still produce a system that meets their needs?”

Introduction (3/3)


Requirements prioritizationRequirements prioritization


Prioritization principles

”Prioritization means balancing the business

benefit of each requirement against its cost and

any implications it has for the architechtural

foundation and future evolution of the product ”

[Wie99]


Why prioritize requirements? (1/2)

Priorities help you

concentrate on the most important user and customer

requirements

focus the development effort

manage projects more effectively

plan for staged deliveries

It can also help you

make acceptable trade-offs among conflicting goals

allocate resources [Wie99], [Kar97]


Why prioritize requirements? (2/2)

”If the customers do not differentiate their requirements by

importance and urgency, project managers must make these

decisions on their own.” [Wie99]

”Most software organisations carry out this selection process informally and quite frequently produce systems that developers, customers and users view as suboptimal.” [Kar97]


Challenges of prioritization (1/2)

Different stakeholders have usually different opinions

about requirement´s importance and urgency.

People naturally have their own interest and they

aren`t always willing to compromise their needs for

someone else`s benefit.

Many of the prioritization methods are either too

complicated and time consuming or insufficient [Rya97].


Challenges of prioritization (2/2)

Customers may try to avoid prioritization,

because

they suspect that low priority requirements

will never be implemented

Developers may try to avoid prioritization,

because

they feel bad to admit, that they can`t

implement all requirements


Prioritization methodsPrioritization methods


Prioritization scales (1/3)

Method

Grouping requirements in the categories

Usually three-level scale (e.g. Essential, Conditional,

Optional [IEEE98])

Participants

Different stakeholders

Conflicts are negotiated ”informally”



Pros

Cheap and easy to use

Clear technique, near common sense.



Cons

The results are in many cases just a rough estimate

Participant dependent method

Customers estimate 85% of requirements at high

priority, 15% at medium and 5% at low priority

No desired flexibility for the project

In the real world low priority requirements have

frequently been abandoned.


Wiegers´ method (1/4)

Basic idea

Customer value depends on both

the benefit provided to the customer by spesific

requirement

penalty paid by that feature [Par96]

Can be used only for negotiable requirements (those

that are not top priority)



Method

Estimate for each requirement using scale from 1 to 9

relative benefit that it provides to the customer

relative penalty the customer would suffer without it

relative cost for it

relative risk for it

Calculate the percentage of the benefit/penalty/

cost/risk that comes from each requirement



Calculate priority for each requirement using the

following formula

Participants

Key customer representatives

Software developers



Pros

Relative method

Estimation is based on several variables

Results are informative and clear

Cons

Not much objective information is available about the

method

Results are dependent on people´s ability to estimate value,

cost and risk


Pair-wise comparison (1/6)

Method

n requirements are setted up in the rows and

columns of the n x n –matrix

Pair-wise comparison of all the requirements

according the criterion from 1 to 9



1 Of equal value

3 Slightly more value

5 Essential or strong value

7 Extreme value

9 Intermediate value



Participants

Requirements engineers

Review candidate requirements

Customers and users

Apply p-w comparison to estimate the relative value of

the candidate requirements

Software engineers

Apply p-w comparison to estimate the relative cost of

implementing each requirement


Value (%)


Cost (%)

RequirementCost-value diagram



Pros

Reliable method

Redundancy

Informative results

Estimating relative values is found to be

easier and quicker than estimating absolute

values



Cons

Suitable only for a small number of requirements

(<20)

Number of comparisons ½ n(n-1)

Does not take dependencies between the

requirements in to account

One needs to get acquainted with the method

before use


Comparison of the methodsComparison of the methods


Comparison of the methods

Prioritization

scales

Wieger`s

method

Pair-wise

comparison

Difficulty Easy Medium Difficult

Work needed Little Medium A lot

Results Rough Clear Clear


References

[Kar97] Karlsson Joachim, Ryan Kevin, “A Cost-Value

Approach for Prioritizing Requirements”, IEEE Software,

pp. 67-74, September/October 1997

[Moi00] Moisiadis Frank, Prioritising Use Cases and

Scenarios, IEEE 2001

[Wie99] Wiegers, K., Software Requirements, Microsoft

Press, Redmond, Washington, 1999.

requirement prioritization

Technology